Current bearing material for gas turbine engines for military use is based on M50 steel. New requirements may be based instead on more corrosion resistant materials manufactured from high chrome alloy steels such as 440C stainless steel and Pyrowear® 675 and Cronidur® 30 as well as hybrid ceramic/metal materials. However, it has been found that the current standard lubricant (tricresyl phosphate (TCP) in a polyolester base) used with M50 steel does not give sufficient wear protection when used with 440C steel.
U.S. Pat. No. 5,422,023 to Francisco teaches an extreme pressure/anticorrosion additive to aviation turbine oils, comprising a 2,5-dimercapto-1,3,4-thiadiazole monomer and an alpha-olefin/maleic ester copolymer. However, in view of advanced corrosion materials now being used in aviation turbines, the requirement for an anticorrosion additive such as the copolymer of Francisco may no longer be necessary. While these thiadiazole monomers are known to impart extreme pressure properties, it has been found (as demonstrated below) that thiadiazole monomer derivatives appear to provide insufficient anti-wear protection when used with corrosion resistant materials such as 440C stainless steel.
U.S. Pat. No. 6,365,557 to Karol teaches additives for imparting extreme pressure properties to lubricating compositions, particularly greases. The additives are the reaction products of 2,5-dimercapto-1,3,4-thiadiazole dimer derivatives with poly(ether)glycols. Such additives would not have been added to lubricating oils because of problems with solubility.
Therefore, an object of the invention is to provide an additive for lubricating compositions, as well as the lubricating oil compositions themselves, which will provide excellent anti-wear performance with respect to corrosion resistant materials.
Another object of the invention is directed toward a method for imparting anti-wear properties to a corrosion resistant material, comprising using the above lubricating compositions described below.